Recently, it has been considered to fabricate high-frequency low-noise amplifiers with an SOI (Silicon On Insulator) CMOS process (hereinafter, an SOI process), in place of an SiGe bipolar process (hereinafter, an SiGe process). This is because the SOI process is a lower cost process than the SiGe process. Moreover, MOS transistors fabricated with the SOI process have small parasitic capacitance and hence suffer small power loss on high-frequency signals.
As one of the methods to achieve a function (gain control function) to control the gain of such a high-frequency low-noise amplifier, it is considered to vary a current supplied to the high-frequency low-noise amplifier. However, varying a supply current may cause the high-frequency low-noise amplifier to exhibit an unstable behavior, such as oscillation, ringing, etc., in part of range or the entire range of the supply current.